1. Field of the Invention
This invention relates to a method of automatically inspecting a solder portion of a printed circuit board or others. This invention also relates to an apparatus for automatically inspecting a solder portion of a printed circuit board or others.
2. Description of the Prior Art
It is known to automatically inspect solder portions of a printed circuit board. In a prior art apparatus, each of solder portions is observed by a camera, and a signal representing an image of the solder portion is generated by the camera. A computer processes the image signal, calculating the values of goodness/poorness judgment factors such as the length, the width, and the area of a dark region or a bright region on the basis of the distribution of the luminance of the image. The calculated values are compared with reference values to decide whether the solder portion is good or poor.
In the prior art apparatus, each of the calculated values of the goodness/poorness judgment factors is subjected to judgment through the comparison with the related reference value. In the case where all the goodness/poorness judgment factors are judged to be acceptable, the solder portion is finally decided to be good. In the case where at least one of the goodness/poorness judgment factors is judged to be unacceptable while the other goodness/poorness judgment factors are judged to be acceptable, the solder portion is finally decided to be poor. Since some of good solder portions have an unacceptable judgment factor although the other judgment factors are acceptable, the final decision regarding the solder portion tends to be low in accuracy.
Some of solder portions are in a gray zone between a good zone and a poor zone. It is generally difficult to execute accurate and reliable decision regarding such gray-zone solder portions. It is better to execute closer inspection of gray-zone solder portions.